Settle a dispute: is it "safe" to take a cool shower after exercising?

Factual evidence – polar bear clubs and Finns who run out of the sauna into a snow or ice bath.
One year I jumped into Lake Michigan twelve consecutive months. I am not dead or even ill.

I say it’s safe based on this: According to the first aid class that I took last year, when someone is over-heated, you want to cool them down, asap. That means cool water and ice baths. On the other hand, if someone is hypothermic, you want to warm them slowly.

I’ve always heard you want to keep your muscles warm after exercising, hence why you see Olympians donning jackets immediately post-event.

Yes, one of the first things a baseball pitcher does when he leaves the field is put ice on his shoulder.

I think a baseball pitcher’s shoulder is kind of an extreme condition though. Doesn’t really seem like a fair comparison.

And apparently the act of icing after pitching is debated.

It’s fine.

My personal feeling is not to shock the body at any time. Then again, polar bear clubs are popular.

In my experience, it is perfectly ‘safe’ to do so, however you will lose some of the benefit of the exercise. As long as you don’t strain yourself afterwards (i.e. don’t do stretching or more exercise after the shower), then you will be perfectly fine, and it won’t cause you any damage. You’d have to do more to your body to seriously disrupt homeostasis.

That said, you will lose some benefits. As @lilikoi said, there’s a reason Olympians put on jackets after an event. Usually mylar, too, which is one of the best materials for heat retention. Allowing your muscles to cool slower allows them more time to slow down their processes, and also allows them more time to adjust to the exertion of the exercise, which means that the exercise session will have a higher impact. Cold water shocks them back to normal temperature, and so they won’t have as much time to grow and reshape themselves to be better at the next exertion.

Also, cooling slowly will help increase flexibility, as the cold water will shock your muscles into contracting, and possibly hurt your flexibility (though not very much), while cooling slowly will again allow your muscles to more naturally contract, and so they will result it having slightly more flexibility then otherwise.

I’m a member of the 200 Club (streaking around the South Pole marker at a delta-T of at least 200F); I’m still around 30 years after initiation. The cold shock is probably not good for people with heart problems. After exercise, I follow the old Roman bath system in the shower: hot, tepid, then cool; keeps the muscles from seizing up.

The only credible problem I’ve heard is that maybe people with bad hearts should be careful.

I’ve done it many times, so, for me it seems to be safe.

A cool shower to cool down is fine. The only concern might be muscle cramping. Cold muscles can cramp up, and if you just exercised, your muscles are fatigued. Just remember to stretch AFTER exercising, and if you never have a muscle cramp problem, then I say it is not a problem.

People every day go from being super hot in the sun, to jumping into a cold refreshing pool or ocean. Bringing your body temperature back down is a good thing. When you exercise your body is working hard to make sure you don’t overheat, a cool shower will help the process.

Very cold ice like water would be bad, but, you said that is not the case.